Research projects

The ability to detect
changes around us, such as the appearance or disappearance of an object, has
far-reaching implications for survival. These processes have received
considerable attention in Vision research. In contrast, the processes by which
listeners detect the appearance or disappearance of objects in busy acoustic
scenes, comprised of many concurrent sources, remain poorly understood.
This is surprising because often it is sound that alerts us to important
changes in the scene: Hearing is sensitive to a much larger space than the
other senses and in many cases we hear change before we see it
(for example, somebody entering the room while your back is to the door; Sudden
quiet from the kids’ playroom indicating they are up to mischief..). Indeed,
the auditory system is commonly assumed to play a key role in the brain’s
change-detection network by serving as an ‘early warning
device’, rapidly directing attention to new events in the scene.

The
present project is classified as ‘basic’ research with the goal of
understanding how listeners with normal hearing detect and process
change-events (appearance or disappearance of sources) in auditory scenes. The
behavioural and functional brain imaging experiments detailed here are designed
to systematically explore listeners’ change detection
behavior, understand the relevant processes and identify their neural
underpinnings: How
are object appearance and disappearance events detected? What brain mechanisms
are involved? Are change events detected automatically by the brain, even when
listeners’ attentional focus is elsewhere? What makes certain change events
fundamentally more salient than others? Under what conditions do listeners
perform well, and which situations result in reduced performance? In busy
scenes, such as those we often face in the environment, behaviourally relevant
scene changes often coincide in time with other events. How resilient are the
auditory change detection mechanisms to irrelevant events occurring at the same
time as the auditory change? Do auditory and visual perturbing events have the
same detrimental effect on performance?

These issues are important from the point of
view of understanding perception and how the brain analyses and represents the
dynamics of our surrounding environment. Furthermore, understanding what makes
certain events pop out and grab attention, while other events go unnoticed is important for
designing human-computer interfaces, and other devices intended to help
professionals (operating room personnel, air traffic controllers, pilots, etc.)
operate effectively in environments where the detection of change is
critical. Additionally, since change
detection is a major contributor to efficient interaction with the environment,
understanding the profile of change detection in normal listeners can provide a
measure against which to evaluate hearing impairment as well as the benefit
obtained from hearing aids.

Sounds we encounter in the
environment are often patterned (regularly repeating). Accumulating evidence suggests that listeners
are very sensitive to these patterns. In
Many cases the auditory brain acquires this structure automatically, independent
of listeners’ attentional state, supported by automatic mechanisms which are continually searching for regularities
within the incoming stimulus and use those to predict future input. These
models, or rules, about how sources in the environment are expected to behave,
thus constitute a dynamically evolving perceptual model of the acoustic
scene. In several ongoing projects,
which are examining different forms of patterning and different listening
contexts. We are interested in identifying what features of sounds we are sensitive to,
how quickly these are learnt, and how this learning is affected by listeners’
attentional and perceptual state. Delineating the operational limits of these
mechanisms is essential to uncovering the neural computations which underlie
sensitivity to sound patterns, and, more broadly, critical to our understanding
of how the dynamics of our acoustic environment are coded by the brain in the
course of scene perception.

An issue at the forefront of research
into auditory processing is understanding how listeners perform figure-ground
segregation. How are we able to extract, and focus attention on a sound of
interest in a background of other interfering sounds (e.g. the voice of a
friend in a noisy party)? Our experiments aim to understand how these processes
are carried out by listeners, which aspects of sound our brains use to achieve segregation, and the
neural systems involved in this process.

Experiments designed to uncover the neural
underpinnings and perceptual limits of selective attention: what aspects of
sound can listeners attend to and the brain mechanisms involved in this process.
What enables us to perceptually pull out a sound of interest out of a mixture
of many sounds (‘the cocktail party problem’)? How is how we listen, affect the way sounds
are processed by the brain?

Experiments aiming to understand what aspects of
auditory processing are susceptible to attentional manipulation. I.e. which processes are automatic, and which
require attention or are affected by the perceptual state and behavioural goals
of the listener. Understanding these processes is important for understanding
what information the brain extracts of the auditory world when our focus of attention
is diverted away from ‘listening’.

This
project aims to understand and quantify auditory salience and distraction in
the context of complex acoustic scenes. Namely, the neural and computational processes
by which concurrently presented sounds compete for, and capture, listeners’ perceptual
and attentional resources. It is widely assumed that the auditory system plays
a critical role in the brain’s ‘early warning system’ by continuously scanning
the unfolding acoustic scene for potentially relevant events (e.g. the approach
of predators or pray) even when attention is focused elsewhere. Characterizing those
acoustic features that attract attention is thus an important aspect of studying
auditory perception in the healthy brain, as well as for understanding how the
system breaks down as a consequence of aging, hearing impairment or certain
neurological disorders (e.g. Schizophrenia) which are characterized by abnormal
auditory processing. Understanding
acoustic salience, and its reverse – distraction, also has immediate
applications in guiding the design of warning systems, hearing aids, human
computer interfaces, and other devices intended to help individuals respond
efficiently to urgent events in their surroundings.

This work is conducted in collaboration with Shigeto Furukawa and Makio Kashino at the human information science laboratory, NTT, Japan